1. Field of the Invention
The present invention is related to media control and, more specifically, media control valves used to control the flow of a media into a fluid stream as part of an apparatus for treatment of a surface.
2. Description of the Related Art
A typical manual media control valve is disclosed in U.S. Pat. No. 4,322,058(“the '058 patent”). The valve of the '058 patent is attached to a media vessel and controls the flow of the media from the media vessel into a conduit containing a fluid stream. This conduit terminates in a nozzle. Fluid and media pass through the nozzle at high speed and are typically used to treat surfaces.
A more recent pneumatic actuated media control valve is the pipe side valve shown and described in U.S. Pat. No. 3,476,440 (“the 440 patent”), issued to Thompson, et al on Mar. 30, 1982. The valve described in this patent has been has been widely accepted in applications where the flow of particulate material, particularly abrasive material, from a tank or hopper, is fed into a blast line for propelling the particulate material or media through a nozzle.
As shown in the '440 patent, the valve has a unitary plunger which is movable axially with respect to a lateral particulate material inlet between positions closing and opening the inlet. The plunger is moved by pneumatic or spring force against the piston. The valve body passage through which the plunger is disposed, and the plunger itself, are formed to have abrasion resistant surfaces. A lateral air pipe nipple sealed to the valve body receives the abrasive material flowing through the valve for use in blasting operations.
Various improvements to the basic media control valve have been proposed. For example, U.S. Pat. No. 5,407,379 (“the '379 patent”) and U.S. Pat. No. 5,401,205 (“the '205 patent”) disclose media control valves having a media passage between the media control valve and the conduit. The media passage converges into a slot-shaped outlet in the conduit so as to reduce the perimeter of the outlet placed perpendicular to air flow and consequently reduce turbulence as air passes across the outlet. The media control valves disclosed in the '205 and '379 patents are particularly useful in metering and dispensing sodium bicarbonate media.
Over the years many modifications to media control valves have been proposed. For example, U.S. Pat. No. 5,810,045 (“the '045 patent”) discloses a pneumatic actuated metering control valve for introducing particulate materials into a high-pressure air stream and suggests several uses for this valve, such as, by way of example, introducing fluid catalytic cracking catalyst particles into fluid catalytic cracking units used to crack and reform various petroleum based products, introducing particulate catalysts into other kinds of chemical processes and spraying particulate ingredients on adhesive substrates as part of various manufacturing processes.
U.S. Pat. No. 5,407,379 (“the '379 patent”) and U.S. Pat. No. 5,401,205 (“the '205 patent”) disclose a pneumatic actuated media control valve having a media passage between the media control valve and the conduit. The media passage converges into a slot-shaped outlet in the conduit so as to reduce the perimeter of the outlet placed perpendicular to air flow and consequently reduce turbulence as air passes across the outlet. The '045 patent also includes the use of multiple seals around a plunger of the valve with an exhaust therebetween to remove any contaminants that breach the seals.
Another type of valve used in the industry is the manual metering valve shown and described in my U.S. Pat. No. 7,549,911, entitled: “Media Control Valve with Pressure Balance Loop”. The valve there shown incorporates a bypass loop for equalizing pressure during startup operation. Specifically, the valve includes a pressure fluid inlet upstream of the valve media outlet. When the valve system is off, the system is typically depressurized. In typical applications, a backflow into the valve is caused by the fact that on startup the pressure increase in the media tank is at a slower rate than the pressure increase in the blast line. Thus, there is a backflow from the blast line into the valve until both the media tank and the blast line pressures are equal. This continues until the valve is again equalized with the media flowing through the valve and into the pressurized fluid stream. The valve so disclosed incorporates a balancing or equalizing pressure loop for minimizing or reducing the backflow of pressurized fluid into the valve through the media outlet port during startup. The valve also includes a cleanout port for cleaning out debris that may obstruct media flow and residue media after use. This permits clean out of the valve without disassembly. The ability to clean out the valve after use further reduces wear and tear on the valve and minimizes maintenance and repair.
Despite the various improvements in myriad valve designs for a variety of applications, the valve disclosed in the Thompson patent is to this day a widely accepted valve for blasting operations. As desirable as this valve is, there remains room for improvement, especially with respect to wear reduction, as well as repair and maintenance of the valve.
One of the most critical issues with remote actuated media control valves is the life of the valve. The abrasive media can damage the valve beyond use in a short period of time, requiring replacement or substantial repair. Many of the valves of the prior art, as particularly shown in the '440 and '045 patents, typically have a sleeve that consists of a hardened liner (tungsten carbide or hardened steel) jacketed with a softer material. In these configurations, the hard liner is jacketed and bonded with stainless steel with the ID of the jacket being flush with the ID of the hard liner. The valve plunger is of the same type construction, except that the jacket is a hard material and the inside is a softer more workable material. It is not uncommon for any of these valves to malfunction after some use due to the sleeve and plunger locking up, thereby not allowing the plunger to reciprocate within of the sleeve. In some cases, solid hardened sleeves are utilized. In either case when plungers lock up or seize, accelerated wear results on the adjacent components of the valve such as the body, seat, and base.
The '045 patent purports to keep particulates from entering the cylinder chamber, and thereby improve the life of the valve. However, this patent does not address the more frequent mode of failure where the plunger binds against the sleeve, or is seized. A gap is required for assembly of the plunger into the sleeve. Any feasible designed gap will allow migration of particles smaller than the gap. In addition, as the plunger and sleeve are abraded, the gap will become progressively larger and allow larger abrasive particles to migrate.
Most, if not all of the prior art valve designs use a plunger sleeve design. All of these valves place the plunger seal(s) above the sleeve. While these designs have been effective at sealing, there are two issues. First is the accessibility of the seals. Many of these valves use a single plunger seal above the sleeve which is relatively easy to access but sometimes requires a user to completely remove the valve to properly replace the plunger seals. More recent valve designs include up to three plunger seals with an external o-ring. At least one prior art valve has four plunger seals with a stainless steel bushing stacked above the sleeve. In many of these valves it is very difficult to change out the seals due to the deep location of the seals with the inherently gritty environment. In valves utilizing the multiple plunger seal design, the plunger seals are stacked on top of each other which is a blind install that does not permit visual verification of proper seal alignment or seal installation. Also, this will create boundaries where two soft surfaces press against each other, and which creates an opportunity for the seals to misalign when stressed during plunger movement or during installation or operation.
It has been determined that this seizing can be attributed to several factors. First, the stainless jacket on the sleeve wears at the ID more quickly than at the hard liner primarily because of the difference in hardness of the two materials. This creates a beveled surface between the sleeve stainless ID and plunger OD where particles would cause binding. Second, the stainless ID section of the sleeve is softer than some of the abrasive media used, such as aluminum oxide grit or hardened steel grit. These harder particles can dig into the relatively softer yet still rigid stainless steel and cause binding between the plunger and sleeve.
Third, this design permits the accumulation of grit within the plunger-to-sleeve gap. The reciprocating motion combined with the location of the plunger, sleeve, and piston of this valve and its many variations results in a scooping effect that over time will bind this type of valve. Each time the valve is actuated, a small amount of grit or abrasives, smaller than the plunger to sleeve gap, is scooped or dragged upward in between the sleeve and plunger. When the pneumatic signal is removed and vented, the plunger returns to the closed position, dragging some of the small grit back but leaves a small residual of grit or abrasives. With each actuation, the residual grit accumulates. After many cycles, the accumulated grit will effectively form a wedge that will bind the OD of the plunger against the ID of the sleeve. Easily crushable mineral abrasives do not cause as much of a problem as more resilient abrasives such as hardened steel grit and Aluminum oxide. This is a problem with all plunger-sleeve designs in the airblast industry regardless of their hardness and regardless of their material composition.
Recently, valve designs including an offset sleeve internal diameter and plunger seals of the spooled sleeve have been designed in an attempt to minimize the issue by not allowing or significantly reducing the accumulation of residual abrasives. In addition, the grit that does bypass the seals is so small that they polish the OD of the plunger and consequently improve the life of the seals above the first one. This is the benefit implementing the aforementioned offset sleeve feature with the spool sleeve seals.
The current state of the art for these types of valve is a piston actuated design where a compressed air signal is used to apply force against a spring counteracted piston sealed with piston seals, both within a cylinder. When the compressed air signal is removed, the spring pushes the piston back to its off position which is generally closed. The plunger which is fastened to the piston is what directly opens and closes the abrasive flow.
The weakness of this design is that it is not tolerant of particulate contamination which is inherent of the dusty and gritty conditions of an airblast environment. This contamination can originate from two sources. First is the ambient environment of the equipment and valve. In the valve as disclosed in the '058 patent, and its many variations, the ambient dust will be sucked in when the piston returns to the off position. As the piston travels to its off position, the volume above the piston increases and must draw air from an ambient source. As the dust and grit laden ambient air is drawn in, so too is the grit. Many of the prior art valves, try to mitigate this by installing breather vents with particulate filtration varying from 15-90 microns. When the breather vent is sized properly, the particulates that pass through and enter the cylinder are not large enough to cause the piston to jam, or seize. Breather vents are an additional cost and properly sized fine breather vents are even more expensive. Some end users have even tried to replace the vents with cheaper larger micron vents and have experienced failures. The second source of grit contamination is from the compressed signal line. Blast systems with inadequately supplied compressed airflow tend to pull grit from the blast pot or vessel and cause dust and grit to eventually contaminate the compressed air control line. Where the first source originates from ambient and will contaminate the cylinder volume above the piston, the second source of contamination will reside below the piston. Both have the potential to bind the piston against the cylinder wall.
Typically, in the prior art designs, the piston and piston seal do not function efficiently and fail quickly without lubrication. The lubrication is required to reduce the piston-to-cylinder friction and reduces the response time of the valve. While lubrication serves to minimize the wear of the piston seal which is required for proper actuation of the valve, its consistency is like paste when applied. In some cases oil or light fluids are used. Both types of lubrication have a tendency to attract dust which can contribute to the piston to cylinder binding.
Many prior art plunger sleeve designs utilize a straight cylindrical sleeve inserted within a straight cylindrical cavity that is slightly larger the outsider dimensions of the sleeve. Inherent to this design, grit will find its way and reside between the outside of the sleeve and inside of the valve body. This will significantly increase the force required to remove the sleeve from the body. Also, due to the straight cylinder and mating cavity, the grit continues to roll and slide which creates friction until the sleeve is completely removed. This makes disassembly relatively difficult.
Many of the prior art valves use variants of a tungsten carbide plunger fused or joined to a stainless shaft with bolt threads to fastened the piston. Generally the wear on these occur due to the sliding and rubbing of the plunger against the inside of the sleeve with abrasive grit between them. Consequently, the wear is mainly in this area. Generally, it has been observed that the stainless portion of the plunger is still in good condition. However, since it is fused to the tungsten carbide, the still new stainless is discarded along with the worn Tungsten.
It is desirable to improve on the various prior art designs by incorporating design changes which facilitate maintenance and repair of the valve. As stated, the primary wear portions of the valve are the plunger and the sleeve. In many prior art valves, the entire plunger assembly must be removed and the valve completely disassembled in order to replace the worn components. Likewise, the sleeve can only be replaced by disassembling the entire valve.
It is desirable to provide a media control valve permitting more cost effective maintenance by reducing the replacement requirements for those components which are not subject to wear, to provide a more effective body gasket and seal system and to permit easier assembly and disassembly.